Showing papers on "Voltage-controlled filter published in 2001"

Specification and design of a prototype filter for filter bank based multicarrier transmission

Abstract: The specifications of filter banks for multicarrier transmission systems with a large number of subchannels are discussed, with application to xDSL and power line communication in mind. The near perfect reconstruction (PR) modulated approach is considered and the importance, for the system, of the prototype filter delay is stressed. An existing design technique known to be particularly relevant to the context is revisited from a frequency sampling perspective. The performance results in terms of subchannel noise floor and delay are given for several filter lengths and an experimental validation is provided. Finally, an improvement to the design technique is proposed, which brings a gain of 3.3 dB in subchannel interference power level.

Method of channel frequency allocation for rf and microwave duplexers

Abstract: A method is provided for operating a duplexer including a first tunable bandpass filter, a second tunable bandpass filter and means for coupling the first bandpass filter and the second bandpass filter to an antenna The method comprises the steps of tuning the first tunable bandpass filter to provide a passband corresponding to an assigned transmit frequency, and tuning the second tunable bandpass filter to provide a passband offset from an assigned receive frequency, when the duplexer is operated in a transmit mode When the duplexer is operated in a receive mode, the first tunable bandpass filter is tuned to provide a passband offset from an assigned transmit frequency and the second tunable bandpass filter is tuned to provide a passband corresponding to the assigned receive frequency

A passive series, active shunt filter for high power applications

Abstract: This paper presents a hybrid series passive/shunt active power filter system for high power nonlinear loads. This work is motivated by the fact that the ability of a converter to perform effectively as an active filter is limited by the power and the frequency distribution of the distortion for which it must compensate. This system is comprised of a three-phase shunt active filter and series AC line smoothing reactance installed in front of the target load. The proposed system significantly reduces the required shunt active filter bandwidth. The space-vector pulse width modulation (PWM) controller is based on a dead-beat control model. It is implemented digitally using a single 16-bit microcontroller. This controller requires only the supply current to be monitored, an approach different from conventional methods. The paper provides background on the operation of the filter, the details of the power circuit, the details of the control design, representative waveforms, and spectral performance for a filter which supports a 15 kVA phase controlled rectifier load. Experimental data indicate that the active filter typically consumes 2% or less of the average load power, suggesting that a parallel filter is an efficient compensation approach. The spectral performance shows that the active filter brings the system into compliance with IEEE519-1992 up to the 33rd harmonic for an AC line smoothing reactance of 0.13 p.u.

Harmonic filtering of high-power 12-pulse rectifier loads with a selective hybrid filter system

Abstract: Current distortion of 12-pulse rectifier loads is significantly lower compared to six-pulse rectifier loads. However, in passive filtering of the lowest and dominant characteristic 11th and 13th harmonics, the use of 5th and 7th filters is often required in order to prevent possible parallel and series resonance between the passive filter and source impedance which can be excited by source background distortion or by load current residual noncharacteristic harmonics at the 5th and 7th harmonic frequencies. In hybrid filter systems, an active filter (AF) can be added in series with the passive filter in order to isolate the source and load. In most proposed hybrid filter systems, AF control is based on the detection of total current distortion and high-frequency inverters. With a selective AF control system and voltage-controlled inverter, the AF can be controlled to isolate the load at the critical frequencies only while at all other frequencies the passive filter function is preserved so that lower switching frequency and AF rating is required. In this paper, the authors present a selective AF filter control system and simple hybrid filter topology suitable for the compensation of high-power 12-pulse rectifier loads. Harmonic current controllers based on the second-order infinite-impulse response digital resonant filters are used, as they can be considered as simple digital algorithms for more complex double cascaded synchronous-reference-frame-based proportional plus integral controllers. They are centered to the targeted harmonic frequencies by using an adaptive fundamental frequency tracking filter. This approach gives good results, even if the reference waveform (in our case, a load voltage) is highly distorted or unbalanced and no separate phaselocked loop is required. Test results for a laboratory model of this system and stability analysis are presented and the importance of delay-time compensation is discussed.

Shunt active filter for power quality improvement

Abstract: This paper describes the development of a low cost shunt active power filter with digital control, which allows dynamic power factor correction and both harmonics and zero-sequence current compensation. The active filter controller is based on the instantaneous power theory (p-q theory) and was implemented using a standard 16 bits microcontroller. The p-q theory is introduced followed by the presentation of some active power filters topologies. Then a brief description of the implemented solution is made, including references to software tools used for simulation and system development. Experimental results are also presented, showing the good performance of the developed active filter.

Design of low-voltage CMOS continuous-time filter with on-chip automatic tuning

Abstract: A technique for designing a low-voltage continuous-time active filter is presented in this paper. In this technique, current sources are added to the inverting or noninverting op-amp terminals such that the op-amp input common-mode voltages can be set close to one of the supply rails to allow low-voltage operation. An automatic frequency and Q tuning technique is proposed for tuning the active filter using programmable capacitor arrays (PCAs). The proposed tuning technique does not require any peak detectors, which are difficult to implement at a low supply voltage. Instead, it uses a few analog comparators, a digital comparator, and a few binary counters to adjust the PCAs. To demonstrate the proposed techniques, a 1-V 1-MHz second-order filter fabricated in a conventional 1.2-/spl mu/m CMOS process is presented. For a 5-kHz input signal, the filter achieves a THD of -60.2 dB for a peak-to-peak output voltage of 600 mV. The frequency tuning range is between 585 kHz and 1.325 MHz. The measured power consumption for the filter alone consumes about 0.52 mW and for the entire system consumes about 1.6 mW for a supply voltage of /spl plusmn/0.5 V.

New current-mode current-controlled universal filter with single input and three outputs

Abstract: In this study, a new current-mode current-controlled universal filter with single input and three outputs is presented. The proposed circuit uses single-output current controlled conveyors (CCCIIs) and can simultaneously realize lowpass, bandpass and highpass filter functions all at high impedance outputs. Realization of notch and allpass responses does not require additional active elements. The circuit enjoys independent current-control of the parameters ω0 and ω0/Q without disturbing the gains of the lowpass, bandpass and highpass filters. Both its active and passive sensitivities are low.

Input filter design for sliding mode controlled matrix converters

Abstract: This paper presents the input filter design for sliding mode controlled matrix converters. A global sliding mode control approach is considered for the converter with input filter to guarantee near unity input power factor operation and voltage or output current control. The sliding surfaces are directly obtained from the global system equations (matrix converter and input filter) written in the phase canonical form. The association of these sliding surfaces with the state-space vectors technique allows the choice of the most appropriate switching strategy. The proposed new input filter design considers the maximum allowed displacement factor introduced by the filter, as well as the ripple present at the capacitor voltages. Simulation results are obtained and discussed.

Sliding-window transform with integrated windowing

Abstract: A system for a sliding-window transform with integrated windowing is described. The system provides a Direct Fourier Transform kernel with an integrated windowing filter having a desired number of stages. In one embodiment, the windowing filter is a lowpass filter. In one embodiment, the lowpass filter has a rectangular filter transfer characteristic. The DFT includes a complex multiplier. A first portion of the windowing filter is provided before the complex multiplier and can be implemented using real arithmetic. A second portion of the windowing filter is provided after the complex multiplier and is implemented using complex arithmetic. In one embodiment, the filter weights of the second portion of the windowing filter are unity and thus no multiplier is needed for the filter weights in the second portion of the windowing filter.

Filter-and-sum beamformer with adjustable filter characteristics

Abstract: We introduce a polynomial filter structure for filter-and-sum beamforming applied to a microphone array application. The structure is a multidimensional extension of the well known Farrow structure, which has mainly been used for fractional delay filtering and interpolation of I-D signals. The proposed method enables an easy, smooth and efficient control of the beamforming filter characteristics by adjusting only a single control variable, e.g., for dynamic beam steering. The optimization method for polynomial beamforming filter design is presented and illustrated with simulations of beamforming filter characteristics. The design example is given for a linear array of four omni-directional microphones and a polynomial FIR filter with 20-tap delay lines.

Novel analytical model for design and implementation of three-phase active power filter controller

Abstract: The paper presents a simple analytical model for the design and implementation of a three-phase active power filter controller. Voltage decouplers and pole-zero cancellation are used in current regulators to simplify the current control plant to a first-order delay type. This simplification is made by considering the delay times caused by the lowpass filter of reference current calculation circuits, line inductors of an active power filter and the feedback circuit of a DC-link voltage. From the derived analytical model, the cutoff frequency of the lowpass filter and controller parameters can be appropriately determined to increase the harmonic current compensating capability of an active power filter and accelerate the dynamic response of the DC-link voltage. Analytical and experimental results indicate that the proposed active power filter can largely improve the total harmonic distortion of current and correct the power factor to unity with balanced and unbalanced loads.

Adaptive spatio-temporal filter for human vision system models

Abstract: An adaptive spatio-temporal filter for use in video quality of service instruments based on human vision system models has a pair of parallel, lowpass, spatio-temporal filters receiving a common video input signal. The outputs from the pair of lowpass spatio-temporal filters are differenced to produce the output of the adaptive spatio-temporal filter, with the bandwidths of the pair being such as to produce an overall bandpass response. A filter adaptation controller generates adaptive filter coefficients for each pixel processed based on a perceptual parameter, such as the local average luminance, contrast, etc., of either the input video signal or the output of one of the pair of lowpass spatio-temporal filters. Each of the pair of lowpass spatio-temporal filters has a temporal IIR filter in cascade with a 2-D spatial IIR filter, and each individual filter is composed of a common building block,5 i.e., a first order, unity DC gain, tunable lowpass filter having a topology suitable for IC implementation. At least two of the building blocks make up each filter with the overall adaptive spatio-temporal filter response having a linear portion and a non-linear portion, the linear portion being dominant at low luminance levels and the non-linear portion being consistent with enhanced perceived brightness as the luminance level increases.

Power line interference removal from electrocardiogram using a simplified lattice based adaptive IIR notch filter

Abstract: We propose the use of a lattice based second order infinite impulse response (IIR) notch filter with a simplified adaptation algorithm for removal of the power line frequency from ECG signals. The performance of this filter is better as compared to a second order infinite impulse response (IIR) notch filter for real time ECG recording systems where the frequency of the line varies over a narrow range about 50 Hz.

A 1.9 GHz Si active LC filter with on-chip automatic tuning

Abstract: The achievable quality factors (Q) of on-chip inductors fabricated with standard Si technology are limited. Inductor Q factors can be enhanced by active means, resulting in GHz-range filters with adequate dynamic range for certain applications. One such application is the replacement of off-chip filters in the transmit part of a wireless transceiver, following a mixer. The limits of the technique are tested here by using it in a filter for the entire band used in the PCS 1.9 GHz standard. A tuning-friendly filter can be built with magnetically coupled LC resonators. Two identical Q-enhanced LC resonators, together with the loading impedances, are used form a balanced 4th-order bandpass filter. The filter and its tuning system are implemented in a 0.25 /spl mu/m BiCMOS technology.

Voltage-mode multifunction filter using one current feedback amplifier and one voltage follower

Abstract: A universal voltage-mode second-order filter with three inputs and one output employing one current feedback amplifier, one voltage follower, two capacitors and two resistors is presented. It offers the following features: realization of allpass, notch, highpass, bandpass and lowpass signals from the same configuration, no requirements for component-matching conditions, orthogonal control of natural frequency and bandwidth, low active and passive sensitivities, minimum active and passive components and cascadability.

Radio receiver having a dynamic bandwidth filter and method therefor

Abstract: A radio receiver (100) has an IF (intermediate frequency) filter (200) for dynamically adjusting its intermediate frequency. The filter (200) includes a filter bank (301), power estimator circuits (308, 310, 312), and weighting circuits (314, 316, 318). The filter bank (301) generates sub-bands, each sub-band having a predetermined frequency range. The power estimators (308, 310, 312) provide an estimated power in each sub-band. A filter control (320) uses the power estimates to determine a percentage of each sub-band signal that is permitted to be coupled a summation circuit (319). The summation circuit (319) sums the weighted sub-band signals to provide a filtered output signal to a demodulator (212).

Method and apparatus for testing frequency-dependent electrical circuits

Abstract: Electrical filter circuits are tested by connecting to the filter inputs without the need to connect to the filter outputs or to disconnect the outputs from a load. A signal generator of known source resistance applies a.c. signals successively over a range of frequencies to the filter inputs, and a voltmeter monitors the voltage across the filter inputs. Different types of filter have different characteristic shapes for the voltage/frequency curve, and processing is applied to the measured results in a compute to determine the location of inflections in the curve and other characteristics of the curve. Methods are disclosed for determining the values of the individual sub-components of the filter. Where the filter is an L-C filter, an interactive process is applied to successively improve the accuracy of the component value determinations. Using the techniques described enables the insertion loss of the filter also to be readily calculated by the computer.

A new characteristics-variable two-input/output filter in D-module-designs, realizations, and equivalence

Abstract: This paper proposes a new n-th order two-input/output filter in a module for two-phase signal processing. The filter can make a distinction between positive and negative frequencies of two-phase signals and can allow one to process the signals based on frequency-polarity. The filter can also change dynamically its filtering characteristics by simply injecting a shift-signal to the filter. Filtering effects equivalent to ones by parallel arranged filters with vector rotators can be obtained, but in a much simpler manner. A total of unified analyses of attractive general properties of the proposed filter is also given for easy designs and realization. The effectiveness of the analyses and usefulness of the filter are examined and confirmed through experiments. The proposed two-input/output filter in module has potential usefulness to a variety of polyphase signal filtering applications including sensorless vector controls of three-phase AC motors that require to process positive or/and negative sequences based on frequency and polarity.

High-frequency filter device, filter device combined to a transmit-receive antenna, and wireless apparatus using the same

Abstract: A high-frequency filter device includes at least one filter to be connected to a high-frequency stage of a wireless apparatus. The filter includes a voltage-controlled variable frequency resonance element which is made of a resonance element and a voltage-controlled variable impedance element electrically connected to the resonance element. The high-frequency filter device includes a control section for controlling a voltage applied to the variable impedance element, and a signal monitoring section for outputting a control signal, with which the voltage is controlled, to the control section based on frequency data as to an oscillating frequency of a local oscillator of the wireless apparatus. The signal monitoring section controls a band frequency of the at least one filter based on the frequency data in such a manner that the band frequency is adaptively changed.

Digital subscriber line (DSL) modem compatible with home networks

Abstract: A cost-effective filter consuming low power and occupying minimal space. The filter may be used in a ADSL modem (or CPE) to filter the signal components other than the ADSL signals. A high pass filter first filters the low frequency components to attenuate (or remove) lower frequency components such as that caused by ADSL transmit echo signals and that used for voice transmission. The high pass filter may be modified by adding a few resistors to limit the voltages of the high frequency signals also. The output of the high pass filter is amplified and passed through a low pass filter to filter the high frequency components (HPNA included). Due to earlier filtering operation of the high pass filter, the signal can be amplified substantially before being sent to the low pass filter. The implementation of the low pass filter is simplified due to the prior amplification.

Frequency-tunable notch filter

Abstract: A new type of frequency-tunable active notch filter achieves frequency selectivity through interaction among input derived signal components that are passed through parallel signal channels in a forward-only direction. The notch filter differs from earlier channelized notch filters by using multiple, instead of just one, bandpass channels that maintain required forward signal flow in the main, passband-determining signal path without signal distortion at passband frequencies. The new approach has been experimentally verified with a hybrid-integrated three-channel filter whose 40-dB-deep band-reject notch can be continuously tuned, with the help of voltage-controlled variable-capacitance elements, from 9.5 to 10.5 GHz. A single-pole bandpass filter tunes in frequency with the help of only one variable capacitance element, yet still maintains constant passband width across the tuning span. One feature of the bandpass filter is the achievement of constant notch bandwidth across the entire frequency-tuning span of the notch filter.

IIR filters based on frequency-response masking approach

Abstract: In this paper, IIR digital filter design based on the frequency-response masking approach is presented. The overall filter structure is based on the periodic model filter, complementary periodic model filter, and masking filters. The periodic model filter is obtained by replacing each delay in the prototype low-pass IIR filter by M delays. Masking filters are designed to eliminate unwanted bands from the periodic model filter or complementary periodic model filter. The transition bandwidth of the overall filter is M times smaller to that of the prototype filter. This technique can be used to design sharp low-pass, high-pass, band-pass, and band-stop filters. IIR model filters are implemented as low-sensitivity wave lattice digital filters (WDF-s) consisting of two all-pass branches in parallel. In all-pass sections, each delay is replaced with M delays to obtain periodic model filter. This way maximal sample frequency of the filter is M times increased. We show that the transfer function of the model filter is an elliptic minimal Q factors (EMQF) filter suitable for the efficient WDF implementation.

A practical triple-mode monoblock bandpass filter for base station applications

Abstract: A practical triple-mode dielectric monoblock band pass filter integrated with a wide bandwidth pre-select mask bandpass filter and a microstrip low pass filter for WCDMA base station application is presented. The dielectric monoblock triple-mode filter was designed and optimized using 3D EM simulation software incorporating the equivalent circuit model. The pre-select filter and low pass filter were used to clean up the spurious response of the triple-mode filter up to 12 GHz. Both triple mode and mask filters are directly mounted on the PCB to minimize the cost and loss.

Input Filter Design

Abstract: It is nearly always required that a filter be added at the power input of a switching converter. By attenuating the switching harmonics that are present in the converter input current waveform, the input filter allows compliance with regulations that limit conducted electromagnetic interference (EMI). The input filter can also protect the converter and its load from transients that appear in the input voltage vg(t), thereby improving the system reliability.

A high frequency bandpass continuous-time filter with automatic frequency and Q-factor tuning

Abstract: A second order high frequency CMOS bandpass filter with automatic frequency and Q-factor tuning is presented. The frequency tuning is based on the phase-locked-loop technique. A new charge pump circuit and a new quality factor tuning scheme are proposed. The circuit was designed using AMI 0.5 u CMOS process. Simulation results of a bandpass filter working at 100 MHz with expected Q of 20 and 50 are presented.

Absorptive filter for semiconductor processing systems

Abstract: In one embodiment, an absorptive filter network is provided between an RF generator and a semiconductor processing reactor. The absorptive filter network includes an absorptive filter circuit which allows energies at a fundamental frequency to pass while absorbing energies at frequencies away from the fundamental frequency. An absorptive filter circuit is located on the reactor-side of the absorptive filter network to isolate the RF generator from the effects of the non-linear loading presented by a plasma in the reactor. Another absorptive filter circuit is located on the RF generator-side of the absorptive filter network to present a stable voltage waveform to the plasma. The absorptive filter network thus minimizes variations in the RF power, and helps prevent fabrication processes from shifting. For applications requiring variable frequency RF power, a filter network having a dissipating circuit is used to minimize RF power variations. The dissipating circuit includes a high-pass filter and a resistive element. The high-pass filter is set at a cut-off frequency above the frequencies of interest (i.e., the frequency range of the supplied RF power). Energies at frequencies below the cut-off frequency are allowed to pass, while energies at frequencies above the cut-off frequency are shunted to the resistive element, where the energies are dissipated.

Tunable filter system with backreflection reference

Abstract: A tunable filter system comprises a signal source providing a WDM having multiple channels, or other signal requiring spectral analysis, within a spectral signal band. A reference signal source is also provided that generates a reference signal with spectral features, such as narrow spectral lines, that are located within a spectral reference band. A tunable filter functions as a band pass filter in transmission and a notch filter in reflection. It is controlled to filter both the reference signal and the WDM signal. A transmission detector is provided to detect the signal transmission through the tunable filter and a return detector is provided to detect the signal that is returned from the filter. Embodiments of the invention rely on a characteristic of a class of tunable filters, such as Fabry Perot etalons, in which light that is not transmitted through the filter is reflected. Thus, while the tunable filter appears as a band pass filter in transmission, it functions as a notch filter in reflection.

Filter Design With Time Domain Mask Constraints: Theory and Applications

Abstract: Optimum envelope-constrained filter design is concerned with time-domain synthesis of a filter such that its response to a specific input signal stays within prescribed upper and lower bounds, while minimizing the impact of input noise on the filter output or the impact of the shaped signal on other systems depending on the application. In many practical applications, such as in TV channel equalization, digital transmission, and pulse compression applied to radar, sonar and detection, the soft least square approach, which attempts to match the output waveform with a specific desired pulse, is not the most suitable one. Instead, it becomes necessary to ensure that the response stays within the hard envelope constraints defined by a set of continuous inequality constraints. The main advantage of using the hard envelope-constrained filter formulation is that it admits a whole set of allowable outputs. From this set one can then choose the one which results in the minimization of a cost function appropriate to the application at hand. The signal shaping problems so formulated are semi-infinite optimization problems. This monograph presents in a unified manner results that have been generated over the past several years and are scattered in the research literature. The material covered in the monograph includes problem formulation, numerical optimization algorithms, filter robustness issues and practical examples of the application of envelope constrained filter design. Audience: Postgraduate students, researchers in optimization and telecommunications engineering, and applied mathematicians.

Automatic filter tuning control system

Abstract: To tune the center frequency of a gm-C filter, which is a bandpass filter with a narrow bandwidth, to a target frequency, only while the filter is being tuned, the original circuit configuration of the filter is replaced with an alternative configuration that realizes a high signal-to-noise ratio. A characteristic tuner generates and inputs an impulse signal, pulse signal or step signal to the filter being tuned and thereby detects and adjusts the center frequency of the filter. And the tuning result is stored on a nonvolatile memory for future reuse. When the filter is operated, the characteristic tuner stops operating to cut down the power dissipation.

Video amplifier for a radar receiver

Abstract: A video amplifier for a radar receiver includes a temperature compensating attenuator. The attenuator includes a temperature sensitive device, such as a thermistor, arranged in a voltage divider network and is coupled in cascade between two filter stages. Each of the filter stages has a bandpass characteristic in order to filter low-frequency leakage signals and provide sensitivity control based on frequency and thus range, while also filtering high frequency signals to reduce aliasing.